J. Curtis Weaver — Page 2

USGS2006

Frequency of annual maximum precipitation in the City of Charlotte and Mecklenburg County, North Carolina, through 2004

A study of annual maximum precipitation frequency in Mecklenburg County, North Carolina, was conducted to characterize the frequency of precipitation at sites having at least 10 years of precipitation record. Precipitation-frequency studies provide information about the occurrence of precipitation amounts for given durations (for example, 1 hour or 24 hours) that can be expected to occur within a specified recurrence interval (expressed in years). In this study, annual maximum precipitation totals were determined for durations of 15 and 30 minutes; 1, 2, 3, 6, 12, and 24 hours; and for recurrence intervals of 2, 5, 10, 25, 50, 100, and 500 years. Precipitation data collected by the U.S. Geological Survey network of raingages in the city of Charlotte and Mecklenburg County were analyzed for this study. In September 2004, more than 70 precipitation sites were in operation; 27 of these sites had at least 10 years of record, which is the minimum record typically required in frequency studies. Missing record at one site, however, resulted in its removal from the dataset. Two datasets--the Charlotte Raingage Network (CRN) initial and CRN modified datasets--were developed from the U.S. Geological Survey data, which represented relatively short periods of record (10 and 11 years). The CRN initial dataset included very high precipitation totals from two storms that caused severe flooding in areas of the city and county in August 1995 and July 1997, which could significantly influence the statistical results. The CRN modified dataset excluded the highest precipitation totals from these two storms but included the second highest totals. More...

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USGS2005

The drought of 1998-2002 in North Carolina — Precipitation and hydrologic conditions

Drought conditions prevailed across much of North Carolina during 1998-2002, resulting in widespread record-low streamflow and ground-water levels in many areas. During this 4-year period, the drought was continuous in areas of western North Carolina, although eastern areas of the State had some periods of relief from tropical storms in 1998 and 1999. The occurrence of dry winters in 2001 and 2002 along with a dry spring in 2002, exacerbated drought conditions across the State and resulted in substantial declines in streamflow and ground-water levels during the summer of 2002. The drought caused widespread hardship and economic losses across North Carolina. During the latter months of 2002, more than 200 municipalities that included most major cities operated under some form of voluntary, mandatory, or emergency water conservation. Reservoirs across North Carolina were at record or near record-low levels, including some of the largest ones used for multiple purposes (flood control, low-flow augmentation, and(or) recreation), and required continuous and careful operation to balance the upstream and downstream needs of users. Precipitation deficits during the 1998-2002 drought for some locations in North Carolina were among the largest documented since the beginning of systematic collection of weather data. The largest deficits occurred primarily in the western Piedmont and were as much as 60 to 70 inches in some locations during the 4-year period. Cumulative monthly precipitation departures for the period May 1998 through September 2002 at 13 selected precipitation sites across the State ranged from 5.3 inches below normal in Greenville (eastern North Carolina) to 66.7 inches below normal in Hickory (western North Carolina). During the 12-month period October 2002 through September 2003, precipitation departures at 7 of the 13 sites were more than 20 inches above normal, primarily in the western Piedmont. Precipitation data for the period of record were examined for 8 of the 13 sites to compare precipitation deficits during the 1998-2002 drought with those that occurred during selected historical droughts. At three of the eight sites (Hickory, Charlotte, and Mocksville), the average monthly deficit for the 1998-2002 drought exceeded the values computed for the other drought periods. Precipitation records for three other sites (Greensboro, Raleigh, and Fayetteville) were adjusted to remove monthly rainfall values associated with several large tropical storms in 1999. The average monthly deficits for the 1998-2002 drought based on adjusted records for these three sites were then determined to be the highest among the drought periods identified during the available periods of precipitation record. Daily mean discharges before and after the drought were compiled for 211 continuous-record gaging stations operated in North Carolina in 2002. Of these 211, 150 stations had periods of record that exceeded 10 years. Among these 150 sites, records of lowest daily mean discharge were set at 65 sites during the 4-year drought (55 sites during the 2002 water year alone). A smaller group of 68 sites having 30 years of uninterrupted record through the 2002 water year and not known to be significantly affected by regulation and(or) diversions was selected for further analyses to quantify the 'daily' percentile and recurrence intervals of 7-day average discharges. Comparisons of minimum 7-day average discharges at six selected gaging stations with long-term records (two from each physiographic province in the State) provided insight into how the 1998-2002 drought compares with previous droughts. At three of the six sites, all located in the Blue Ridge and Piedmont Provinces, the minimum 7-day average discharges during the 1998-2002 drought became the minimum flows of record. One of these three sites, the French Broad River at Asheville, has the longest period of discharge records in North Carolina. These comparisons confirmed that th

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USGS2003

Low-flow characteristics and profiles for the Rocky River in the Yadkin-Pee Dee River basin, North Carolina, through 2002

An understanding of the magnitude and frequency of low-flow discharges is an important part of protecting surface-water resources and planning for municipal and industrial economic expansion. Low-flow characteristics are summarized for 12 continuous-record gaging stations and 44 partial-record measuring sites in the Rocky River basin in North Carolina. Records of discharge collected through the 2002 water year at continuous-record gaging stations and through the 2001 water year at partial-record measuring sites were used. Flow characteristics included in the summary are (1) average annual unit flow; (2) 7Q10 low-flow discharge, the minimum average discharge for a 7-consecutive-day period occurring, on average, once in 10 years; (3) 30Q2 low-flow discharge; (4) W7Q10 low-flow discharge, which is similar to 7Q10 discharge but is based only on flow during the winter months of November through March; and (5) 7Q2 low-flow discharge. The Rocky River basin drains 1,413 square miles (mi 2 ) of the southern Piedmont Province in North Carolina. The Rocky River is about 91 miles long and merges with the Yadkin River in eastern Stanly County to form the Pee Dee River, which discharges into the Atlantic Ocean in South Carolina. Low-flow characteristics compiled for selected sites in the Rocky River basin indicated that the potential for sustained base flows in the upper half of the basin is relatively higher than for streams in the lower half of the basin. The upper half of the basin is underlain by the Charlotte Belt, where streams have been identified as having moderate potentials for sustained base flows. In the lower half of the basin, many streams were noted as having little to no potential for sustained base flows. Much of the decrease in base-flow potential is attributed to the underlying rock types of the Carolina Slate Belt. Of the 19 sites in the basin having minimal (defined as less than 0.05 cubic foot per second) or zero 7Q10 discharges, 18 sites are located in the lower half of the basin underlain by the Carolina Slate Belt. Assessment of these 18 sites indicates that streams that have drainage areas less than about 25 square miles are likely to have minimal or zero 7Q10 discharges. No drainage-area threshold for minimal or zero 7Q10 discharges was identified for the upper half of the basin, which is underlain by the Charlotte Belt. Tributaries to the Rocky River include the West Branch Rocky River (22.8 mi 2 ), Clarke Creek (28.2 mi 2 ), Mallard Creek (41.2 mi 2 ), Coddle Creek (78.8 mi 2 ), Reedy Creek (43.0 mi 2 ), Irish Buffalo/Coldwater Creeks (110 mi 2 ), Dutch Buffalo Creek (99 mi 2 ), Long Creek (200 mi 2 ), Richardson Creek (234 mi 2 ), and Lanes Creek (135 mi 2 ). In the 20-mile reach upstream from the mouth (about 22 percent of the river length), the drainage area increases by 648 mi 2 , or about 46 percent of the total drainage area as a result of the confluences with Long Creek, Richardson Creek, and Lanes Creek. Low-flow discharge profiles for the Rocky River include 7Q10, 30Q2, W7Q10, and 7Q2 discharges in a continuous profile with contributions from major tributaries included. At the gaging stations above Irish Buffalo Creek and near Stanfield, the 7Q10 discharges are 25.2 and 42.3 cubic feet per second, corresponding to 0.09 and 0.07 cubic feet per second per square mile, respectively. At the gaging station near Norwood, the 7Q10 discharge is 45.8 cubic feet per second, equivalent to 0.03 cubic foot per second per square mile. Low-flow discharge profiles reflect the presence of several major flow diversions in the reaches upstream from Stanfield and an apparent losing reach between the continuous-record gaging stations near Stanfield and Norwood, North Carolina.

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USGS2003

Methods for Estimating Peak Discharges and Unit Hydrographs for Streams in the City of Charlotte and Mecklenburg County, North Carolina

Procedures for estimating peak discharges and unit hydrographs were developed for streams in the city of Charlotte and Mecklenburg County in response to a need for better techniques for characterizing the flow of streams. The procedures presented in this report provide the means for estimating unit hydrographs as part of the process used in watershed modeling and(or) design of stormwater-management structures. The procedures include three statistical relations for use in estimating storm peak discharge, unit-hydrograph peak discharge, and unit-hydrograph lag time. A final component of the procedures is the development of a dimensionless unit hydrograph developed from streamflow and rainfall data collected during the 1995-2000 water years at 25 streamgaging stations and up to 60 raingages in the city and county. The statistical relation to estimate the storm peak discharge is based on analyses of observed peak discharges regressed against rainfall and basin characteristics using a database of 412 observations from 61 storm events among the 25 gaging stations. The rainfall characteristics included basin-average rainfall amounts as well as estimates of the maximum and minimum storm rainfall in the basin. The basin characteristics consisted of land-use information and other physical basin characteristics, such as drainage area, channel length, channel slope, percentage of impervious area, and percentage of the basin served by detention. The analyses resulted in a relation that can be used for estimating storm peak discharge based on drainage area, basin-average rainfall, and impervious area. Average unit hydrographs were developed for 24 of 25 streamgaging stations, using from three to nine storms at each site. The average unit hydrograph for each station was converted into four classes of unit hydrographs with durations corresponding to one-fourth, one-third, one-half, and three-fourths of the station-average lag time. For 23 sites, the lag-time-duration hydrographs were then translated into dimensionless unit hydrographs by dividing time ordinates by the lag time and discharge ordinates by peak discharge. For each lag-time-duration class, the dimensionless unit hydrographs for the sites were combined to create an average dimensionless unit hydrograph. The four average dimensionless unit hydrographs were later tested (with estimates of unit-hydrograph peak discharges and lag times) for selection of an overall dimensionless unit hydrograph to be used at ungaged sites in the study area. The two sites where the procedures did not produce unit hydrographs that could be included in the development of the overall dimensionless unit hydrograph had the smallest drainage areas among the sites used in the investigation. The statistical relations for estimating unit-hydrograph peak discharge and lag time were developed by regressing the dependent variables against explanatory variables that describe the basin characteristics. The statistical analyses resulted in a relation for use in estimating a unit-hydrograph peak discharge based on the drainage area. The estimation of the unit-hydrograph lag time is based on the drainage area and percentage of land use in the basin classified as 'woods/brush.' Both relations have coefficients of determination (R2 values) of 0.9 or better. The three components for estimating a unit hydrograph are the dimensionless unit hydrograph and two statistical relations for estimating the unit-hydrograph peak discharge and lag time. These components were applied by using each of the four lag-time-duration average dimensionless unit hydrographs to determine which would be selected as the final overall dimensionless unit hydrograph for streams in the city of Charlotte and Mecklenburg County. Comparisons of the simulated and observed hydrographs were based on the following: (1) hydrograph width at 50 percent of the peak discharge, (2) hydrograph width at 75 percent of the peak discharge, (3) peak discharge

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USGS2001

Watershed characteristics rating for North Carolina

This web site contains the Federal Geographic Data Committee-compliant metadata (documentation) for digital data produced for the North Carolina, Department of Environment and Natural Resources, Public Water Supply Section, Source Water Assessment Program. The metadata are for 11 individual Geographic Information System data sets. An overlay and indexing method was used with the data to derive a rating for unsaturated zone and watershed characteristics for use by the State of North Carolina in assessing more than 11,000 public water-supply wells and approximately 245 public surface-water intakes for susceptibility to contamination. For ground-water supplies, the digital data sets used in the assessment included unsaturated zone rating, vertical series hydraulic conductance, land-surface slope, and land cover. For assessment of public surface-water intakes, the data sets included watershed characteristics rating, average annual precipitation, land-surface slope, land cover, and ground-water contribution. Documentation for the land-use data set applies to both the unsaturated zone and watershed characteristics ratings. Documentation for the estimated depth-to-water map used in the calculation of the vertical series hydraulic conductance also is included.

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USGS1999

Relation of Land Use to Streamflow and Water Quality at Selected Sites in the City of Charlotte and Mecklenburg County, North Carolina, 1993-98

Streamflow and water-quality data were collected at nine sites in the city of Charlotte and Mecklenburg County, North Carolina, during 1993–97. Six of the basins drained areas having relatively homogeneous land use and were less than 0.3 square mile in size; the other three basins had mixed land use. Atmospheric wet-deposition data were collected in three of the basins during 1997–98. Streamflow yield varied by a factor of six among the sites, despite the fact that sites were in close proximity to one another. The lowest yield occurred in a residential basin having no curbs and gutters. The variability in mean flow from these small, relatively homogeneous basins is much greater than is found in streams draining basins that are 10 square miles in size or larger. The ratio of runoff to rainfall in the developing basin appears to have increased during the study period. Low-flow suspended-sediment concentrations in the study basins were about the same magnitude as median stormflow concentrations in Piedmont agricultural basins. Sediment concentrations were higher in the mixed land-use basins and in the developing basin. Median suspended-sediment concentrations in these basins generally were an order of magnitude greater than median concentrations in the other five basins, which had stable land use. Some of the highest total nitrogen concentrations occurred in residential basins. Total nitrogen concentrations detected in this study were about twice as high as concentrations in small Piedmont streams affected by agriculture and urbanization. Most of the total nitrogen consisted of organic nitrogen at all of the sites except in two residential land- use basins. The high ammonia content of lawn fertilizer may explain the higher ammonia concentration in stormflow from residential basins. The two basins with the highest median suspended-sediment concentrations also had the highest total phosphorus concentrations. Median total phosphorus concentrations measured in this study were several times greater than median concentrations in small Piedmont streams but almost an order of magnitude less than total phosphorus concentrations in Charlotte streams during the late 1970's. Bacteria concentrations are not correlated to streamflow. The highest bacteria levels were found in 'first-flush' samples. Higher fecal coliform concentrations were associated with residential land use. Chromium, copper, lead, and zinc occurred at all sites in concentrations that exceeded the North Carolina ambient water-quality standards. The median chromium concentration in the developing basin was more than double the median concentration at any other site. As with chromium, the maximum copper concentration in the developing basin was almost an order of magnitude greater than maximum concentrations at other sites. The highest zinc concentration also occurred in the developing basin. Samples were analyzed for 121 organic compounds and 57 volatile organic compounds. Forty-five organic compounds and seven volatile organic compounds were detected. At least five compounds were detected at all sites, and 15 or more compounds were detected at all sites except two mixed land-use basins. Atrazine, carbaryl, and metolachlor were detected at eight sites, and 90 percent of all samples had measurable amounts of atrazine. About 60 percent of the samples had detectable levels of carbaryl and metolachlor. Diazinon and malathion were measured in samples from seven sites, and methyl parathion, chlorpyrifos, alachlor, and 2,4-D were detected at four or more sites. The fewest compounds were detected in the larger, mixed land-use basins. Residential basins and the developing basin had the greatest number of detections of organic compounds. The pH of wet atmospheric deposition in three Charlotte basins was more variable than the pH measured at a National Atmospheric Deposition Program (NADP)site in Rowan County. Summer pH values were significantly lower than pH measured during the remainder of the year, probably as a result of poorer air quality and different weather patterns during the summer. Concentrations of ammonia and nitrate at the Charlotte sites generally were lower than those measured at the NADP site. Summer concentrations of ammonia and nitrate at both the Charlotte and the NADP sites were significantly greater than concentrations measured during the remainder of the year, again probably reflecting poorer summertime air-quality conditions. Sediment yields at the nine sites ranged from 77 tons per square mile per year in a residential basin to 4,700 tons per square mile per year at the developing basin. Residential areas that have been built-out for several years and industrial areas appear, in general, to have the lowest sediment yields for the Charlotte study sites. Average annual yields of total nitrogen loads ranged from about 1.7 tons per square mile to 6.6 tons per square mile. Average annual total phosphorus yields for all sites except the developing basin were less than 1.4 tons per square mile. Phosphorus yield at the developing basin was 13 .4 tons per square mile per year. Biochemical oxygen demand loading in 1993 from all of the permitted wastewater-treatment facilities in Charlotte and Mecklenburg County was about 1.5 tons per day or 548 tons per year. Converting this point-source loading to an annual yield for the 528 square-mile area of Mecklenburg County is equivalent to 1.03 tons per square mile per year, or a yield much lower than any of the yields measured at the nine study sites. In other words, biochemical oxygen demand loading from nonpoint sources in Mecklenburg County probably exceeds loading from all point sources by a large amount. Loads and average annual yields were computed for five metals-chromium, copper, lead, nickel, and zinc. The highest annual average yields for all five of these metals were in the developing basin, which also had the highest annual average suspended-sediment yield of all the sites. Estimated wet-deposition watershed loadings suggest that atmospheric deposition may be an important source of some metals, including chromium, copper, lead, and zinc, in Charlotte storm water. Storm water from residential land-use basins has higher concentrations of total nitrogen, fecal coliform bacteria, and organic compounds than do other land-use types. Reductions in suspended-sediment concentrations should generally result in reduced export of phosphorus and metals. Stable land uses, such as industrial areas and built-out residential basins, have lower sediment concentrations in stormwater than do mixed land use and developing basins. Finally, atmospheric deposition may be an important source of nitrogen and some metals in Charlotte stormwater.

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USGS1997

Low-flow characteristics and profiles for the Deep River in the Cape Fear River basin, North Carolina

An understanding of the magnitude and frequency of low-flow discharges is an important part of protecting surface-water resources and planning for municipal and industrial economic expansion. Low-flow characteristics are summarized for 7 continuous-record gaging stations and 23 partial-record measuring sites in the Deep River Basin in North Carolina. Records of discharge collected through the 1995 water year are used. Flow characteristics included in the summary are (1) average annual unit flow; (2) 7Q10 low-flow discharge, the minimum average discharge for a 7-consecutive-day period occurring, on average, once in 10 years; (3) 30Q2 low-flow discharge; (4) W7Q10 low-flow discharge, similar to 7Q10 discharge except only flow during the months of November through March is considered; and (5) 7Q2 low-flow discharge. The potential for sustained base flows in the upper half of the basin is higher than that for streams in the lower half of the basin. Much of the decrease in base-flow potential in the lower part of the basin is attributed to the underlying rock types of the Triassic basin. Soils in the lower part of the basin consist of clays which limit the infiltration of water into surficial aquifers for later release to streams during drought conditions. Correspondingly, many streams in the lower part of the basin have minimal (defined as less than 0.1 cubic foot per second) or zero 7Q10 discharges. Drainage area and low-flow discharge profiles are presented for the Deep River. The drainage-area profile shows downstream increases in basin size. At the mouth, the drainage area for the Deep River is 1,441 square miles. Low-flow discharge profiles for the Deep River include 7Q10, 30Q2, W7Q10, and 7Q2 discharges in a continuous profile with contributions from major tributaries included.

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USGS1996

Low-flow characteristics and profiles for selected streams in the Roanoke River basin, North Carolina

An understanding of the magnitude and frequency of low-flow discharges is an important part of protecting surface-water resources and planning for municipal and industrial economic expansion. Low-flow characteristics are summarized for 22 continuous-record gaging stations in North Carolina (19 sites) and Virginia (3 sites) and 60 partial-record gaging stations in the North Carolina Roanoke River Basin. Records of discharge collected through the 1994 water year are used. Flow characteristics included in the summary are (1) average annual unit flow, (2) 7Q10 low-flow discharge, the minimum average discharge for a 7 consecutive-day period occurring, on average, once in 10 years; (3) 30Q2 low-flow discharge; (4) W7Q10 low-flow discharge, similar to 7Q10 discharge except that flow during November through March only is considered; and (5) 7Q2 low-flow discharge. The potential for sustaining base flows is moderate to high in the western part of the basin as well as in the eastern and western fringes of the Piedmont and Coastal Plain physiographic provinces, respectively. Areas of low potential for sustaining base flow exist in the central part of the basin (between eastern Caswell County and western Warren County), where soils have low infiltration rates, and in lower regions of the Coastal Plain, where small streams tend to have zero flow during prolonged drought. Drainage area and low-flow discharge profiles are presented for 10 streams in the Roanoke River Basin in North Carolina and reflect a wide range in basin size, characteristics, and streamflow conditions. The selected streams are Town Fork Creek, Hogans Creek, Mayo River, Buffalo Creek, Smith River, Country Line Creek, Dan River, Marlowe Creek, Hyco River, and Roanoke River. The drainage-area profiles show the increases in drainage areas as streams travel their course in the basin. At the mouths of streams profiled, the drainage areas range from 22 miles to about 9,700 miles. Low-flow discharges for each stream include 7Q10, 30Q2, W7Q10, and 7Q2 discharges in a continuous profile with contributions from major tributaries included.

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USGS1993

Bathymetry of Lake Michie, Durham County, North Carolina, 1990-92

This map report presents the results of a bathymetric survey conducted as part of a 1990-92 study on the effects of sedimentation on Lake Michie, located in northeastern Durham County, North Carolina. Bathymetric data collected at the lake during 1990-92 indicate that, under normal pool conditions at the spillway elevation of 341.0 feet above sea level, the storage volume is 11,070 acre-feet, and the surface area is 508.7 acres. The maximum depth recorded in the lake was 75 feet at approximately 500 feet upstream of Lake Michie Dam.

North Carolina↗